x86/vvmx: Switch nested MSR intercept handling to use struct vmx_msr_bitmap

x86/vvmx: Switch nested MSR intercept handling to use struct vmx_msr_bitmap

Rename vmx_check_msr_bitmap() to vmx_msr_is_intercepted() in order to more
clearly identify what the boolean return value means.  Change the int
access_type to bool is_write.

The NULL pointer check is moved out, as it doesn't pertain to whether the MSR
is intercepted or not.  The check is moved into nvmx_n2_vmexit_handler(),
where it becomes a hard error in the case that ACTIVATE_MSR_BITMAP is set.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>